1. Field of the Invention
The present invention relates to an agitated continuous casting apparatus.
2. Description of the Related Art
There is a conventionally known agitated continuous casting apparatus including a spout having an upward-turned molten metal receiving port and a downward-turned molten metal outlet, a cylindrical water-cooled casting mold disposed immediately below the spout to cool a molten metal from the molten metal outlet, and an agitator for applying an electromagnetic agitating force to the molten metal in the spout.
A continuous casting material is used, for example, as a thixocasting material. In carrying out a thixocasting process, a procedure is employed which comprises subjecting a casting material to a heating treatment to prepare a semi-molten casting material having solid and liquid phases coexisting therein; transferring the semi-molten casting material to a pressurizing-type casting machine; and thereafter charging the semi-molten casting material into a cavity of a casting mold under pressurization. In this case, such a measure is employed, for example, that a substantially short columnar casting material is used, and in the heating treatment, the short columnar casting material is placed in a raised state into a high-frequency coil, and at the transferring step, an outer periphery of the semi-molten casting material is grasped by a clamping member.
For this purpose, it is required that the thixocasting material show a uniform softening property in its entirety at a relatively low temperature, namely, has a good rheologic property and an excellent shape-maintaining property in its semi-molten state.
The spout in the known apparatus has an inside radius r1 which is uniform over its entire length, and the water-cooled casting mold has an inside radius r2 set, e.g., in a range of r2xe2x89xa7r1+20 mm. This is because if r2 less than r1+20 mm, a difference between the temperatures of an upper portion of the water-cooled casting mold and a lower portion of the spout close to the upper portion is small. For this reason, even if the molten metal is brought into contact with the water-cooled casting mold, it is not solidified and as a result, a large number of crystallized products having a high melting point in the molten metal flows back toward the molten metal inlet along the inner peripheral surface of the spout due to their viscosity, making it not possible, to carry out the casting.
However, if the relationship between both the inside radii r1 and r2 is set in the range of r2xe2x89xa7r1+20 mm, as described above, a large difference is produced between the temperatures of the upper portion of the water-cooled casting mold and the lower portion of the spout close to the upper portion. For this reason, the molten metal is liable to be quenched by the water-cooled casting mold to produce dendrite in the outer periphery of a continuous casting material. Such a material suffers from a problem that while it has a good shape-maintaining property in its semi-molten state due to the presence of the dendrite, the softening property of the outer periphery is degraded, resulting in a poor rheologic property.
There is also a conventionally known agitated continuous casting apparatus of the above-described type, which includes a cylindrical water-cooled casting mold having a vertically turned axis and a plurality of cooling water ejecting bores provided through a lower portion of a peripheral wall of the casting mold, and a cylindrical partition wall surrounding the cylindrical water-cooled casting mold to define a cooling water sump around an outer periphery of the cylindrical water-cooled casting mold, and an agitator for applying an agitating force to a molten metal in the cylindrical water-cooled casting mold for causing the molten metal to flow in a circumferential direction.
The vibration due to the agitating force is generated in the cylindrical water-cooled casting mold. When this vibration is not suppressed sufficiently, there is a possibility of a phenomenon bringing about that an unsolidified portion in an ingot breaks through a solidified portion in an outer periphery of the ingot, namely, a situation that a break-out is generated to make the casting impossible. In order to avoid such situation, a measure to strengthen the cylindrical water-cooled casting mold and its support structure is commonly employed.
However, if such a measurers employed, the following new problem is encountered: the cylindrical water-cooled casting mold and its support structure are increased in size and complicated, and this in turn causes an increase in size of the entire apparatus and an increase in manufacture cost.
Accordingly, it is an object of the present invention to provide an agitated continuous casting apparatus of the above-described type, wherein a continuous casting material having a good rheologic property and an excellent shape maintaining property in its semi-molten state can be obtained.
To achieve the above object, according to a first aspect and feature of the present invention, there is provided an agitated continuous casting apparatus comprising a spout having an upward-turned molten metal receiving port and a downward-turned molten metal outlet, a cylindrical water-cooled casting mold disposed immediately below the spout to cool a molten metal from the molten metal outlet, and an agitator for applying an electromagnetic agitating force to the molten metal in the spout so as to rotate the molten metal in a circumferential direction, wherein the agitator cooperates with the spout to form, in the spout, an upper area for permitting the molten metal to move in a substantially radiate direction while permitting it to rotate in the circumferential direction, and a lower area for permitting the molten metal to rotate in the circumferential direction, the spout having an upper area forming portion at an inner peripheral surface thereof, the upper area forming portion being formed into a tapered shape with an inside diameter thereof gradually increasing from its upper peripheral edge toward its lower peripheral edge in order to move, toward the lower area, the molten metal that is in the substantially radiate direction and collided against the upper area forming portion at the inner peripheral surface of the spout.
In the upper area, a large number of crystallized products having a high melting point are produced. The large number of crystallized products in the molten metal moved from the upper area to the lower area are spheroidized in the lower area under an agitating action rotating in the circumferential direction, and are moved in a large amount toward the outer periphery side by a centrifugal force. Thereafter, the molten metal is cooled by the water-cooled casting mold. During this time, the movement of the crystallized products of the high-melting point from the upper area to the lower area is being conducted ceaselessly and hence, the back flow of the crystallized products of the high-melting point from the lower area to the upper area is not produced.
In the continuous casting material produced in the above manner, the large number of the crystallized products of the high-melting point existing in the outer periphery have been spheroidized and hence, the outer periphery shows a softening property similar to that of the main portion excluding the outer periphery. Therefore, the continuous casting material has a good rheologic property. Because the large number of the crystallized products of the high-melting point exist in the outer periphery, the continuous casting material exhibits an excellent shape-maintaining property in its semi-molten state by a shape retention effect provided by the crystallized products of the higher-melting point.
It is another object of the present invention to provide an agitated continuous casting apparatus of the above-described type, wherein the vibration of the cylindrical water-cooled casting mold due to the agitating force can be suppressed by a simple measure.
To achieve the above object, according to a second aspect and feature of the present invention, there is provided an agitated continuous casting apparatus comprising a cylindrical water-cooled casting mold having a vertically turned axis and a plurality of cooling water ejecting bores provided through a lower portion of a peripheral wall of the casting mold, a cylindrical partition wall surrounding the casting mold to define a cooling water sump around an outer periphery of the cylindrical water-cooled casting mold, and an agitator for applying an agitating force to a molten metal in the cylindrical water-cooled casting mold for causing the molten metal to flow in a circumferential direction, wherein a rubber-like elastomeric member having an impact resilience R in a range of 10%xe2x89xa6Rxe2x89xa640% is interposed between the cylindrical water-cooled casting mold and the cylindrical partition wall.
The rubber-like elastomeric member is defined to include an elastomeric member formed of a rubber, an elastomeric member formed of a plastic, and the like. The impact resilience R is determined according to an equation, R=(H1/H0)xc3x97100 (%), wherein H1 represents a height to which a sphere of a constant load is bounded up when the sphere is dropped freely onto the surface of the rubber-like elastomeric member.
The rubber-like elastomeric member having the impact resilience R defined as described above suppresses the vibration of the cylindrical water-cooled casting mold due to the agitating force. Thus, the generation of a break-out can be prevented to advance the casting operation smoothly.
If a solidified product has been deposited on an inner surface of the cylindrical water-cooled casting mold, the rubber-like elastomeric member permits a partial deformation of the cylindrical water-cooled casting mold in a radially outward direction based on the impact resilience, when the molten metal flowing under the action of the electromagnetic agitating force collides against the solidified product. This causes the speed of the cooling water ejected from the ejection bore by compression of the cooling water sump to be increased, thereby increasing the flow rate. Therefore, the cooling of the ingot is conducted rapidly and hence, the molten metal in the vicinity of the solidified product is also solidified or brought into a semi-molten state. Therefore, the solidified product is taken into the ingot being dropped and is thus peeled off from the inner surface of the cylindrical water-cooled casting mold. In a state in which the solidified product has been deposited on the inner surface of the mold, a recessed trace is formed on the outer peripheral surface of the ingot to produce a casting defect.
If the impact resilience R of the rubber-like elastomeric member is in a range of R greater than 40%, the vibration suppressing effect is obtained to reduce the generation of break-out, because the rubber-like elastomeric member shows the resilience substantially similar to that of a metal member, but the recessed trace is liable to be produced, because the deformation permitting effect is not obtained. On the other hand, if R less than 10%, substantially the same state is achieved as in a case where the rubber-like elastomeric member is not interposed between the cylindrical water-cooled casting mold and the cylindrical partition wall. For this reason, the generation of the break-out is increased, and the deformation permitting effect is excessive, whereby the flow of cooling water is damped up and hence, the recessed trace is liable to be produced.
The above and other objects, features and advantages of the invention will become apparent from the following description of the preferred embodiment taken in conjunction with the accompanying drawings.